About target.$triple + target.'cfg()' in cargo config

Cargo Book says:

# Similar for the $triple configuration, but using the `cfg` syntax.
# If several `cfg` and $triple targets are candidates, then the rustflags
# are concatenated. The `cfg` syntax only applies to rustflags, and not to
# linker.

In my Cargo.toml I added a feature:

featureA = [...]

In my .cargo/config I added:

linker = "ld.lld"
rustflags = [
    "-C", "link-arg=-Tlink.ld",
    "-C", "panic=abort"

[target.'cfg(feature = "featureA")']
rustflags = [
    "-C", "target-cpu=cortex-a72",
    "-C", "lto=yes"

target = "aarch64-unknown-none"

And I build all as

cargo xbuild --release --features featureA

Rust flags from [target.'cfg(feature = "featureA")'] are not applied. Maybe it's because of [build] specifying the exact target? How to properly make config and run cargo build so that rustflags are concatenated from target triple and selected features?